The Schott Foundation for Public Education, based in Cambridge, Mass., found a slight improvement since its last study of the issue: While 55 percent of black males in the class of 2004 did not graduate in four years, that figure was 58 percent for the class of 2002.

The new study looked at how states and districts stack up in graduating black and white male students. Among the worst state rates were in Florida, which graduated only 31 percent of its black male students in four years, and in Nevada, which did so with 32 percent. Arizona had the highest rate, 85 percent.

States and districts were also examined for gaps in the rates at which white and black male students graduate on time. Wisconsin, for instance, had a gap of 47 percent, graduating 38 percent of its black male students in four years, compared with 84 percent of its white male students.

The study also found black male students to be underrepresented among students taking Advanced Placement courses, and overrepresented among those classified as having special needs.